The present disclosure is related to methods of monitoring and regulating a xerographic marking device by use of patches, for example inter-document zone (IDZ) control patches, printed in the image area of a photoreceptor device. However, the methods disclosed herein are not restricted to IDZ patches and can be applied to patches printed in an image area and either transferred to paper or sent directly to a toner cleaning mechanism.
In copying or printing systems, such as a xerographic copier, laser printer, or ink-jet printer, a common technique for monitoring the quality of prints is to create a test patch or patch of toner of a predetermined desired density. Therefore, if the density is not at the desired set point, it can be measured and the system can be adjusted to yield the proper density. The actual density of the printing material (toner or ink) in the test patch can then be optically measured to determine the effectiveness of the printing process in placing this printing material on the print sheet.
In the case of xerographic devices, such as a laser printer, the surface that is typically of most interest in determining the density of printing material thereon is the charge-retentive surface or photoreceptor, on which the electrostatic latent image is formed and subsequently, developed by causing toner particles to adhere to areas that are charged in a particular way. In such a case, the optical device for determining the density of toner on a test patch, which is often referred to as a “densitometer” (a reflective sensing device), or a light transmissive sensing device, is disposed along the path of the photoreceptor, directly downstream of the development of the development unit. There is typically a routine within the operating system of the printer to periodically create a test patch of a desired density at predetermined locations on the photoreceptor by deliberately causing the exposure system to charge or discharge as necessary the surface at the location to a predetermined extent.
A test patch is then moved past the developer unit and the toner particles within the developer unit are caused to adhere to the test patch electrostatically. The denser the toner on the test patch, the darker the test patch will appear in optical testing. The developed test patch is moved past a densitometer or a transmissive device disposed along the path of the photoreceptor, and the light absorption of the test patch is tested. The more light that is absorbed by the test patch, the denser the toner on the test patch.
Xerographic test patches are traditionally printed in the inter-document zone (IDZ) on the photoreceptor during an evaluation. They are used to measure the disposition of toner on paper to measure and control the tone reproduction curve (TRC). Currently, most test patches include a solid, mid tone, and highlight patch for evaluation. Unfortunately, the longer the length of each test patch, the more the amount of toner is needed in order to run these tests. Consequently, the larger the test patch, the larger the IDZ needs to be, which results in less job throughput and more toner wasted because the toner in the test patch does not appear on the actual print.
Furthermore, the collection and application of a photoreceptor clean belt profile is both complex and problematic in terms of verifiability, reliability, and timeliness of the updates. Currently, a clean belt profile is performed at start up. The information may be obtained and then stored for later clean belt profiles to compare results; however, not only can using an older clean belt value introduce calibration error, this is a slow process that may need to be repeated several times throughout the life of the device. If it is determined that the photoreceptor has drifted beyond a set point, during cycle up, a collection of the clean belt profile is time consuming. Additionally, the clean belt profiles must be matched with reads in real time so that any read timing errors that exist can be translated into a sensor and therefore color calibration errors.